The conception of a purely muscular insufficiency of the atrioventricular valves is so new a one, that here in America, at least, it has made but little impression upon the great body of physicians who have to do with heart cases. The purpose of this paper is to endeavor, in some small way, to secure for this very important and common group of cases the recognition they deserve, and this not only theoretically but practically at the bedside.

DEFINITION OF MUSCULAR INSUFFICIENCY.A muscular mitral insufficiency is one in which the valves are anatomically normal, in which the mitral ring is not of such large size that the curtains do not suffice to close it, but in which the valve is incompetent, because of the imperfect functionating of the muscular apparatus of the valve.Until very recently we have been accustomed to think of the closure of the valve as